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From: chased@rbbb.Eng.Sun.COM
Newsgroups: comp.lang.misc
Subject: Errors in postings
Message-ID: <2622@exodus.Eng.Sun.COM>
Date: 13 Nov 90 01:41:39 GMT
Sender: news@exodus.Eng.Sun.COM
Reply-To: chased@rbbb.Eng.Sun.COM ()
Organization: Sun Microsystems, Inc.  Mt. View, Ca.
Lines: 32
Suumary: Proof by example that Dan Bernstein is fallible


brnstnd@kramden.acf.nyu.edu writes:
> I quote an article of mine from April:

: Hmmm, this doesn't sound right. After all, if A and B could be aliased,
: and B and C could be aliased, then A and C could be aliased. (This is
: why the natural keyword is ``alias,'' not ``noalias.'')

> I have always held the same position. You can see exactly the same
> position in many of my articles, and in my complaint that the Convex
> anti-aliasing mechanism makes the opposite assumption.

But, this is not correct.  Consider the example:

  extern void f(int * x, int * y, int * z);

  int a[3],b[3];
  ...
  f(a,a,b);
  f(a,b,b);
  ...

If you attempt to derive one summary for the aliasing that might
hold upon entry to "f" (i.e., without cloning specialized copies),
you discover that

  x may-alias y
  y may-alias z
  x NOT-alias z

David Chase
Sun Microsystems